There are a number of liquid dispensing systems on the market. Beer taps are a common application of such dispensing systems which attempt to accurately dispense predetermined quantities of beer. The dispensing of a predetermined quantity of beer is referred to as a pour. Generally these systems comprise the following characteristics:
a user interface means which is used to preselect a quantity of beer, as desired; PA1 a user activated means which initiates the pour; PA1 a faucet means which controls the flow of beer from a pressurized source; PA1 an actuator which is connected to the faucet means for opening and closing of the faucet means; PA1 a flowmeter which is located in-line between the faucet means and the beer source to provide a measure indicative of the quantity of beer which passes through the faucet means; and PA1 a programmable controller means which calculates the cumulative volume of beer dispensed, and produces a signal for closing of the faucet means, when a quantity of beer equal to the preselected quantity has been dispensed.
In U.S. Pat. No. 5,022,557 issued to Turner, a typical programmable controller, electromechanical beer dispensing system is disclosed. In Turner's system, conventional mechanically activated handle and faucet have been replaced with electronic switch means to achieve precise control of the dispensing action. The quantity of beer is cumulatively calculated during a pour using a flow metering means. The quantity of beer is continually compared against a look-up table of desired dispensed quantities by a programmable controller and a signal is generated to terminate the flow of beer when the desired quantity has been dispensed. A solenoid, associated with the faucet, receives the signal and acts to close off the flow of beer.
Turner does not necessarily achieve an accurately dispensed quantity of beer. There are physical and process aspects of the dispensing system which introduce variability in the quantities ultimately dispensed. Physical limitations of the faucet and the actuating means result in a delay in their response. After having received a command to close, the faucet permits a residual spilled quantity of beer to be discharged as it closes. An attempt to offset the look-up table value by the amount of the spill fails to compensate reliably. Changes in the physical condition and response of the faucet, and process variability, such as the pressure of the beer source, dynamically affect the quantity of the spill.
In another aspect, Turner does not permit an operator to repeatedly interrupt and re-start the flow of liquid without losing track of the cumulative quantity of beer dispensed. Beer dispensed prior to an interruption is designated as waste. Particularly with respect to dispensing beer, foaming can occur which can be controlled somewhat by temporarily interrupting the flow. The apparatus of Turner comprises an actuating electrical solenoid associated with the faucet which tends to warm the exiting beer, further exacerbating foaming.
When the liquid being dispensed, such as beer, has a significant commercial value, and is dispensed frequently in small quantities, the effect of the residual spill quantity can be economically significant and detrimental.
It is therefore an object of the invention to provide means for accurately dispensing a preselected quantity of liquid in spite of repeated interruption and re-starting of the liquid flow, having accounted for variable spill quantity.
It is a further object of the invention to provide a beer dispensing system which uses a traditional beer tap handle to activate the system and yet still achieve an accurate pour.